Two paediatric cancer patients were found to have influenza shortly after receiving chemotherapy. Both presented with neutropenic fever. The first patient, a 15-year-old boy with Hodgkin's lymphoma, recovered without complications. The second patient, a 15-month-old-girl with metastatic Wilms' tumour, died due to severe infectious complications. These cases illustrate that common viruses, such as the influenza virus, can cause fulminant secondary infections in immunocompromised patients. Viruses, including the influenza virus, should always be considered as pathogens in patients with neutropenic fever, and influenza vaccination should be considered in these high-risk patients.